Hematopoietic progenitor kinase 1 (HPK1) originally cloned from hematopoietic progenitor cells is a member of MAP kinase kinase kinase kinases (MAP4Ks) family, which includes MAP4K1/HPK1, MAP4K2/GCK, MAP4K3/GLK, MAP4K4/HGK, MAP4K5/KHS, and MAP4K6/MINK (Hu, M. C., et al., Genes Dev, 1996. 10(18): p. 2251-64). HPK1 is of particular interest because it is predominantly expressed in hematopoietic cells such as T cells, B cells, macrophages, dendritic cells, neutrophils, and mast cells (Hu, M. C., et al., Genes Dev, 1996. 10(18): p. 2251-64; Kiefer, F., et al., EMBO J, 1996. 15(24): p. 7013-25). HPK1 kinase activity has been shown to be induced upon activation of T cell receptors (TCR) (Liou, J., et al., Immunity, 2000. 12(4): p. 399-408), B cell receptors (BCR) (Liou, J., et al., Immunity, 2000. 12(4): p. 399-408), transforming growth factor receptor (TGF-βR) (Wang, W., et al., J Biol Chem, 1997. 272(36): p. 22771-5; Zhou, G., et al., J Biol Chem, 1999. 274(19): p. 13133-8), or Gs-coupled PGE2 receptors (EP2 and EP4) (Ikegami, R., et al., J Immunol, 2001. 166(7): p. 4689-96). As such, HPK1 regulates diverse functions of various immune cells.
HPK1 is important in regulating the functions of various immune cells and it has been implicated in autoimmune diseases and anti-tumor immunity (Shui, J. W., et al., Nat Immunol, 2007. 8(1): p. 84-91; Wang, X., et al., J Biol Chem, 2012. 287(14): p. 11037-48). HPK1 knockout mice were more susceptible to the induction of experimental autoimmune encephalomyelitis (EAE) (Shui, J. W., et al., Nat Immunol, 2007. 8(1): p. 84-91). In human, HPK1 was downregulated in peripheral blood mononuclear cells of psoriatic arthritis patients or T cells of systemic lupus erythematosus (SLE) patients (Batliwalla, F. M., et al., Mol Med, 2005. 11(1-12): p. 21-9). Those observations suggested that attenuation of HPK1 activity may contribute to autoimmunity in patients. Furthermore, HPK1 may also control anti-tumor immunity via T cell-dependent mechanisms. In the PGE2-producing Lewis lung carcinoma tumor model, the tumors developed more slowly in HPK1 knockout mice as compared to wild-type mice (see US 2007/0087988). In addition, it was shown that adoptive transfer of HPK1 deficient T cells was more effective in controlling tumor growth and metastasis than wild-type T cells (Alzabin, S., et al., Cancer Immunol Immunother, 2010. 59(3): p. 419-29). Similarly, BMDCs from HPK1 knockout mice were more efficient to mount a T cell response to eradicate Lewis lung carcinoma as compared to wild-type BMDCs (Alzabin, S., et al., J Immunol, 2009. 182(10): p. 6187-94). These data, in conjunction with the restricted expression of HPK1 in hematopoietic cells and lack of effect on the normal development of immune cells, suggest that HPK1 is a drug target for enhancing antitumor immunity. Accordingly, there is a need for new compounds that modulate HPK1 activity.